The present invention relates to a pressure difference driven adsorption process in which a more preferentially adsorbed component of a gaseous mixture is adsorbed in an adsorbent under pressure to rectify the gaseous mixture. The adsorbent is regenerated by subjecting the adsorbent to a sufficiently low partial pressure of the more preferentially adsorbed component of the gaseous mixture. More particularly, the present invention relates to such a method in which the adsorbent is divided into two portions and each portion is subdivided into serially-connected sections to more efficiently utilize the adsorbent.
A common pressure difference driven adsorption process is pressure swing adsorption in which two or more beds are employed in an out of phase relationship so that an on-line bed adsorbs a more preferentially adsorbed component of a mixture to be separated while an off-line bed is being regenerated. Such processes have wide spread application to the separation of atmospheric gases. In such an application, each of the beds has an adsorbent formed of molecular sieve material designed to more preferably adsorb either oxygen or nitrogen. The air is passed into the on-line bed where for instance, nitrogen is adsorbed to produce a product stream highly enriched in oxygen. Since air, by in large, contains oxygen and nitrogen, the product stream can contain oxygen with small amounts of argon and trace amounts of other elements. A point is reached at which the adsorbent becomes saturated with the more preferentially adsorbed component and therefore must be regenerated. At this point, the on-line bed is brought off-line and the previously regenerated off-line bed is brought on-line. The previous on-line bed is vented to atmosphere and then subjected to a sufficiently low partial pressure of the more preferentially adsorbed component of the mixture. This causes desorption of the more preferentially adsorbed component from the adsorbent bed. Thereafter, just prior to the off-line bed being brought on-line, it is backfilled with the product stream so as to be slowly brought up to operating pressure.
A common problem that is encountered in conducting a pressure driven adsorption process is that the portion of the bed at which the mixture to be separated enters becomes saturated rather quickly, while an opposite portion of the bed, through which the product stream is expelled, is never fully saturated. As a result, a large mass of the adsorbent must be used if extremely high purities are to be achieved. As will be discussed the present invention solves this problem by utilizing the adsorbent in a more efficient manner so that high purity product streams can be produced while using a lower amount of adsorbent as compared with the amount of adsorbent that would have to be used in an equivalent prior art process.